Frequency dividing apparatus



1947- J. c. COYKENDALL 15 FREQUENCY DIVIDING APPARATUS Filed Oct. 9, 1942 SOURCE OF NEGATIVE PULSES /5 A; UTILIZATION DEV/CE Invenbor': John C..Coy}senda| I His Atbor-ne Patented Feb. 18, 1947 FREQUENCY DIVIDING APPARATUS John C. Coykendall, Bridgeport, Conn., assignor to General Electric Company, a corporation of New York Application October 9, 1942, Serial No. 461,382

6 Claims.

My invention relates to frequency dividing apparatus and particularly to such apparatus of the cycleor pulse-counting type including a condenser charged by pulses at the impressed frequency and discharged periodically to provide pulses at the desired lower frequency.

It is an object of my invention to provide a frequency dividing apparatus including an improved arrangement for obtaining stability over a wide range of frequencies.

It is another object of my invention to provide an improved frequency dividing apparatus the operation of which is terminated immediately when the input signal is removed.

Another object of my invention is to provide a frequency dividing apparatus including an improved arrangement for providing uniform pulses to operate the apparatus regardless of wide variations of the amplitude of the pulses impressed on the input of the apparatus.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 diagrammatically represents one form of a frequency dividing apparatus embodying my invention, and Fig. 2 is a curve illustrating the operating characteristics of a portion of the apparatus shown in Fig. l.

Briefly, the apparatus illustrated in the drawing comprises an electron discharge device or amplifier tube for providing energy pulses and arranged to charge two condensers in series during each pulse. One of the condensers is a small variable capacitor or trimmer which may be adjusted to determine the number of pulses required to provide a predetermined charge in a corresponding number of steps on the other or main condenser. At the end of each pulse the trimmer is discharged. A discharge circuit is provided for the main condenser and comprises a pair of electron discharge devices connected to provide a modified multi-vibrator, the main condenser on which the charge is accumulated being connected between the control grid of one of the devices and the anode of the other so that when a predetermined charge has been collected the state of the currents in the two devices is reversed and a pulse is produced at the output of the apparatus, the apparatus thereupon being returned to its normal condition for accumulating another charge on the main condenser. The amplifier tube upon which the input pulses are impressed is operated at such a point in its plate voltage plate current characteristic that changes in tube characteristics have little, if any, effect on the frequency dividing apparatus, and tubes may be interchanged during service Without requiring readjustment of the circuit elements to maintain the desired frequency division.

Referring now to the drawing, the frequency divider shown in Fig. 1 comprises a beam type amplifier tube or electron discharg device H! having a control element or grid ll coupled through a resistor l2 and condenser is to an apparatus or circuit 14 which supplies periodic negative energy pulses of a predetermined frequency. The device I 0 includes a cathode l5 and beam plates IS, an anode I1 and a screen grid Hi. The anode I1 is connected to the positive side of a suitable source of voltage, as indicated at H], through a plate or anode resistor 20, and the screen I8 is connected to the positive side of a source of screen voltage, as indicated at 2|.

The division of frequency is obtained by charging and discharging a condenser 22 once for each successive group of pulses comprising a predetermined number of the pulses impressed on the apparatus. The circuit for discharging the condenser 22 comprises a modified multivibrator including electron discharge devices 23 and 2 arranged in a common envelope 25. The device 23 includes a cathod 26, a control electrode 2'! and an anode 23, and the device 24 includes a cathode 29, a control electrode and an anode 3|. The cathodes 26 and 29 are connected to ground and the negative side of the anode voltage source through a common resistor 33. The anodes 28 and 3| are connected to the positive side of the source of anode voltage I9 through resistors 34 and 35, respectively. 'Anode 28 of the device 23 is coupled to the control electrode 30 of the device 24 through a resistor 36, and the control electrode 30 is connected to ground through a resistor 31. The anode 31 of device 24 is coupled to the control electrode 21 of the device 23 by means of the condenser 22. For negative potentials the control electrode 21 is connected to ground through a cathode 38, an anode 39, a cathode 40 and an anode 41 of an electron discharge device 42 of the double diode type. It will be evident, therefore, that th control element 2! cannot be negative with respect to ground as any charge at such potential would be conducted to ground through the 'device 42. Control electrode 21 is, therefore,

normally at zero or ground potential or at some slight positive potential which, however, is insufficient to overcome the bias due to the drop in the resistor 33 produced by the current flowing in the device 24 which draws both grid and anode current. It will thus be seen that the device 23 is normally non-conducting and the device 24 normally conducting. The condenser 22 is coupled to th anode ll of the electron discharge device lfl through a small variable condenser is and cathode 38 and anode 39 of the device 42. When a negative pulse is impressed on the con rol element i! of the device It a positive pulse appears at the anode I! and the con densers 4. 3 and 22 are charged in series because of the difference in potential between the anode H and the potential at the anode 3! of the device 24. As soon as the positive pulse disappears the condenser d3 is discharged through cat ode t and anode 4! of the device Q2. The condenser 22, however, cannot be discharged since the device 42 is non-conducting for positive potentials on the cathode 38. It is evident that each successive positive pulse produced by the device it charges the condensers 43 and 22 in series, the charge added to the condenser 22 be-- ing progressively smaller because of the charge previously accumulated. When a predetermined charg has accumulated in a plurality of steps on the condenser 22 the bias on the grid 2? produced by the drop across the cathode resistor 33 reduced sufiiciently to render the device 23 conducting. The voltage at the anode 28 thereupon ialls due to the drop in resistor 36 and the control element 30 of the tube 2 becomes negative and finally cuts off the current flowing through the device 24. The plate of the condenser 22 attached to control electrode 2? is thereupon raised to a higher positive potential because of the reduction in voltage drop in the resistor 35; the grid 21, therefore, becomes highly positive causing the device 23 to draw grid current. This grid current discharges condenser 22. This, in turn, reduces the potential of the control element 2'! substantially to that of the cathode it, and the voltage at the plate or anode 28 rises because of the decreased drop in the resistor 34. The rise in voltage causes an increase in positive potential at the control element 39 of the device 2d and the device '24 again becomes conducting and plate and grid current again start flowing therethrough. The state of currents in the devices 23 and 24 is now, again, reversed, the grid 21' being driven negative by the increased drop in resistor 35. However, the negative potential is removed since the element Z'i is connected directly to ground for negative potentials through the electrodes 38; e9, 43 and ll of the device 42. The discharge circuit comprising devices' 23 and 26 is thereby returned to starting condition whereupon a charge may again be accumulated on condenser 22.

An output circuit or utilization device 44 is coupled to the anode 28 of the device 23 and an energy pulse is impressed upon the utilization circuit each time the condenser 22 is discharged in the manner described above. The duration of the pulse at the output of the divider is-determined by the size of the condenser 22 and by the values of the several resistors 33, 34, 35, 3S and 37. In the foregoing description it has been assumed that the duration or width of the discharge pu se is. less than the ime between successive pulses impressed upon. the input of the apparatus. A wider pulse may be used, however, in a manner which will be explained later.

The dynamic characteristics of the discharge device I l are selected so that it produces uniform positive pulses andutilizes almost the entire available plate supply voltage. The plate or anode resistance 2B is relatively high with respect to the normal plate resistance for the dis charge device it! and is selected so that the load line of the device it] falls below the knee of the Zero grid potential curve on the plate currentvoltage characteristic of the tube as shown in Fig. 2 where the load line is indicated at 68 and thezero grid potential curve at 49. The full plate supply voltage is indicated at point 5i! where the load line intersects the zero current axis of the curve and the operating point of the discharge device for zero grid potential is at the point 5! where the load lin intersects th curve 49. It is, therefore, evident that between the points 58 and 5! almost the entire voltage is employed when the plate current varies from its value at 5! to zero. The curve 59 of Fig. 2 as illustrated is that of a type 6V6-GT beam power amplifier. For purposes of comparison the zero grid poten: tial curve of a receiving pentode type GSJ'? has been shown at 5'2, and with the same load line the operating point of this tube would occur at 53, it being apparent that a relatively small portion of the available plate supply voltage is employed for producing positive pulses. When the operating point 5% lies below the knee of the zero grid potential curve 49 considerable change in grid potential may occur without a noticeable change of plate current. Furthermore, the operi ating point 5! lies in a region of the character istic curve where there can be very little, if any, noticeable difference between plate current when different tubes of the same type are substituted in the circuit. Consequently the operation of the discharge device ill with the load line 48 assures reliable operation of the frequency dividing, apparatus without the necessity of readjusting it each time it becomes necessary to replace the tube I E). When the discharge device H3 is, operated on the characteristic indicated in Fig. 2 excellent clipping is obtained at both ends of; the grid excursion when a negative pulse is impressed on the control grid. In other words, a clean-cut pulse is obtained. It. will readily be apparent to. those skilled in the art that even a positive grid potential can result in little, if any, change in plate current since all the grid potential curves within a wide region must pass through the operating point 5| which lies in the so-called diode region of the tube characteristic.

Beam power tubes other than the 6V6-GT and also certain pentode output tubes may be operated to obtain the above desired characteristics; it being necessary, of course, that a tube be selected which can be operated-with its load line intersecting the zero grid potential curve below the knee thereof and preferably in the so-called diode region which is essentially a straight line over a relatively wide range of. grid potential.

Increased stability for high divisions of frequency may be obtained, particularly where a relatively narrow range of driving frequency is to be impressed on the apparatus by adjusting the duration or width of the discharge pulse so that two or more driving-pulses are impressed on the input of theapparatus during the period Of a single discharge pulse. The increased duration of the dischar e pulse may-be obtaineclrby increasing the capactiy of the condenser 22. The

effect of the driving pulses impressed on the input grid ll during the discharge pulse is neutral Zed by the flow of grid current in the discharge device 23. It follows that when the con denser 22 is again conditioned to receive a charge the complete charge must be acquired during the remaining pulses of the successive group of pulses impressed on the apparatus during each output cycle. The charge on the condenser 22 can, therefore, be built up in larger increments and greater over-all stability is obtained. Furthermore, the setting of the variable condenser 43 for any given frequency division becomes less critical as the duration of the discharge pulse is increased. When the discharge pulse has a duration equal to two or more of the impressed pulses the dividing apparatus will not operate over as wide a range of driving or impressed pulse frequencies. This is due to the fact that, for a given division of frequency, there must always be the same number of pulses neutralized by the grid current flowing in the discharge device 23, and if this number of pulses is changed the division of frequency or count of the divider will also be changed.

My invention provides a frequency dividing apparatus which is of simple construction and may be employed for divisions of frequency within a wide range. By way of illustration only and not by Way of limitation there are listed below values of circuit constants which have been found to be suitable for the circuit of Fig. l. which was designed to divide by live a frequency of 3,000 cycles per second. The device ID was a type 6V6-GT beam power amplifier; the device 1 42 a 61-16 double diode and the device 25 a GSN'l- T twin triode.

Resistor l2 ohms 220,000 Resistor 20 do 20,000 Resistor 33 d0 15,000 Resistor 34 do 56,000 Resistor 35 do 56,000 Resistor 36 do 56,000 Resistor 3! do 150,000 Capacitor i3 mmf 470 Capacitor 43 (maximum) rnmf Capacitor 22 mmf l 390 With the above constants the circuit operated so F that the duration of the discharge pulse was less than a single cycle of the frequency of the impressed pulses. t was found that the circuit was not critical for changes in positive voltage applied to the terminal 59; this is probably due to the fact that the bias on the discharge device 23 varies with the applied voltage as well as do the pulses applied at the output of the device Iii. A series of frequency dividers constructed as shown in Fig. 1 have been connected for reducing a frequency of 15 kilocycles per second to a frequency of about 60 cycles per second, and the count or division of frequency did not change when the line voltage or positive potential applied at the terminal H! was varied as much as fifty per cent.

Although I have illustrated one embodiment of my invention employing an electron discharge device of the beam power amplifier type and an output discharge tube comprising two electron discharge devices in a single envelope, other modifications will readily occur to those skilled in the art. For example, the discharge device l0 may be any suitable output discharge device or amplifier of the pentode type comprising a suppressor grid instead of the beam forming plates of the beam power amplifier, and discharge devices having separate envelopes may be em ployed instead of device 25. Therefore, it will be appreciated that I do not wish to be limited to the particular embodiment of my invention disclosed herein, and that I contemplate in the appended claims to cover all modifications which fall within the true spirit and scope of my invention.

What I claim as new and desire to secure'by Letters Patent of the United States is:

1. In a frequency dividing apparatus, two electron discharge devices each having an anode, a cathode and a control electrode, means for coupling the anode of one of said devices to the control-electrode of the other of said devices, a condensercoupling the anode of said other device to the control electrode of said one device, means for rendering said other device normally conducting and said one device normally non-conducting, and means dependent upon the impressing on the input of said apparatus of a predetermined number of energy pulses for charging said condenser in a plurality of steps to a potential sufficient to render said one device conducting and thereby reverse the state of currents through said devices and produce a pulse of energy at the output of said apparatus.

2. A frequency dividing apparatus comprising two electron discharge devices each having an anode, a cathode and a control electrode, separate resistances for connecting the anodes of said de vices to the positive side of a voltage source, a common resistance connecting the cathodes of both said devices to the negative side of the source, means coupling the anode of one of said devices and the control electrode of the other of said devices, means for rendering said other device normally conducting and said one device normally non-conducting, a condenser coupling the control electrode of said one device and the anode of said other device, means for impressing periodic energy pulses on said apparatus and for collecting a predetermined charge on said condenser duringthe period when a predetermined number of said pulses are impressed on said apparatus whereby the potential of the control electrode of said one device is raised sufiiciently to render said one device conducting to reverse the state of currents through said devices and to produce one energy pulse at the output of said apparatus for each successive group of pulses comprising said predetermined number of pulses impressed on said apparatus.

3. A frequency dividing apparatus comprising two electron discharge devices each having an anode, a cathode and a control electrode, resistances for connecting the anodes of said devices to the positive side of a source of voltage, a common resistance connecting the cathodes of both said devices to the negative side of the voltage source, a resistance coupling the anode of one of said devices and the control electrode of the other of said devices, a resistance connecting the control electrode of said other of said devices to ground, a condenser connected to couple the anode of said other device and the control electrode of said one device, means for impressing periodic energy pulses on said apparatus, means for collecting a predetermined charge on said condenser during the period when a predetermined number of said energy pulses are impressed on said apparatus to raise the potential of the control electrode of said one device sumciently to render said one device conducting to reverse the state of currents through said devices and to produce one energy pulse at the output of said apparatus for each successive group of pulses comprising said predetermined number of pulses impressed on said apparatus.

4. In a frequency dividing apparatus, two electron discharge devices each having an anode, a cathode and a control electrode, means for coupling the anode of one of said devices to the control electrode of the other of said devices, a condenser coupling the anode of said other de vice to the control electrode of said one device, means for rendering said other device normally conducting and said one device normally nonconducting, means including a third electron disimpressed upon said apparatus are necessary to charge said condenser to said potential.

5. In a frequency dividing apparatus, two electron discharge devices each having an anode, a cathode and a control electrode, means for coupling the anode of one of said devices to the control electrode of the other of said devices, a

condenser coupling the anode of said other device to the control electrode of said one device, means for rendering said other device normally conducting and said one device normally nonconducting, means including a third electron discharge device connected to receive periodic energy pulses and to produce energy pulses in a positive direction at its output, means including a second condenser for connecting the output of said third device and the control electrode of said one device whereby said condensers are charged in series by the pulses produced at the output of said third device, means for discharging said second condenser after each of said pulses, the capacities of said condensers being such that said first mentioned condenser is charged in a plurality of steps by a predetermined number of said pulses to a potential suiiicient to render said one device conducting and thereby reverse the state of currents through said two devices and produce a pulse of energy at the output of said apparatus.

6. In a frequency dividing apparatus two electron discharge devices each having an anode, a cathode and a control electrode, means for coupling the anode of one of said devices to the control electrode of the other of said devices, a condenser coupling the anode of said other device to the control electrode of said one device, means for rendering said other device normally conducting and said one device normally non-conductin and means dependent upon the impressing on the input of said apparatus of a predetermined number of energy pulses for charging said condenser by a plurality of steps to a potential sufficient to render said one device conducting and thereby reverse the state of currents through said devices and produce a pulse of energy at the output of said apparatus, the capacity of said 0011- denser being such that the duration of the pulse produced at the output of said apparatus is equal to that of a plurality of the pulses impressed upon the input of said apparatus whereby the full charge of said condenser is produced by less than the total of said predetermined number of pulses.

JOHN C. COYKENDALL.

REFERENCES CITED The iollowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,050,059 Koch Aug. 4, 1936 2,221,452 Lewis Nov. 2, 1940 

